This project is concerned with a study of the effect of glucocorticoid steroids in two strains derived from HeLa cells. The emphasis is placed on those biochemical alteration that concern membrane cholesterol and phospholipids. It is believed that in the HeLa strain S3G, the glucocorticoid-induced changes in lipid composition are followed by modulation of the activity of some membrane associated enzymes, including alkaline phosphatase. In another strain (S3K) which is more resistant to glucocorticoids in terms of changes in lipid metabolism, the enzyme fluctuations appear to be either lacking or are of a different nature. The two HeLa strain which also have different characteristics with regard to their growth dynamics serve as a model for studying those hormonal controls that are reflected in modified behavior of the cell surface in a culture system. BIBLIOGRAPHIC REFERENCES: Melnykovych, G., Standaert, M. M., Matthews, E. R. and Gray, S. L. (1976) Corticosteroids and phosphatidylcholine biosynthesis in microscomal fractions from L 5128 Y lymphoma. Cancer Research 36:1545-1550. Melnykovych, G., Matthews, E., Gray, S. L. and Lopez, I. (1976) Inhibition of cholesterol biosynthesis in HeLa cells by glucocorticoids. Biochem. Biophys. Res. Communs. 71:506-512.